Two-stage rotodynamic blood pump

ABSTRACT

A pump includes a housing, a stator supported in the housing, and a rotor assembly including a rotor supported in the housing for rotation relative to the stator about an axis. The stator includes a stator core, a first lamination wound around an axial portion of the stator core, and a second lamination wound around a second axial portion of the stator core. The first and second laminations are spaced from each other along the length of the stator core. The rotor includes a rotor core, a first magnet assembly that extends around an axial portion of the rotor core, and a second magnet assembly that extends around a second axial portion of the rotor core. The first and second magnet assemblies are spaced from each other along the length of the rotor.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.12/720,953, which was filed on Mar. 10, 2010, now U.S. Pat. No.8,210,829 B2, which is a continuation-in-part of U.S. application Ser.No. 11/789,205, filed on Apr. 24, 2007, now U.S. Pat. No. 7,704,054 B2,which claims the benefit of U.S. Provisional Application Ser. No.60/795,096, filed on Apr. 26, 2006.

GOVERNMENT RIGHTS

The invention described in this application was supported, at least inpart, by United Stated Government Contract No. NIH 1R01HL096619-01A1with the National Institutes of Health.

TECHNICAL FIELD

The present invention relates to a pump that may be used in fluidhandling applications where two fluid streams are to be balanced. Moreparticularly, the present invention relates to a two-stage rotodynamicpump configuration for providing pulsatile, continuous flow, bloodpumping performance.

BACKGROUND OF THE INVENTION

Congestive heart failure (CHF) is an increasingly common cause ofcardiovascular disability and premature death. Despite advances inmedical therapy, heart transplant is the primary course of action fortreating patients with end-stage congestive heart failure. Because theavailability of donor organs is limited, however, CHF patients may beforced to wait until a suitable donor organ is located. Blood pumpingdevices, referred to as ventricular assist devices (VADs) and totalartificial hearts (TAH), can be used as a bridge-to-transplant option inorder to save patients with CHF and other cardiac conditions whootherwise would not survive until a suitable donor organ is located.Ultimately, such blood pumping devices will become viable as permanentor long-term alternatives to transplant.

SUMMARY OF THE INVENTION

The present invention relates to a valveless, sensorless, pulsatile,continuous flow total artificial heart that can self balance left andright circulation, without electronic intervention, by acting as aninlet pressure balancing regulator as it pumps. Left and rightcirculations are impelled via a single moving part, which revolveswithin a brushless, sensorless DC motor winding. This rotating assemblyis free to move axially in response to the hydraulic environment,thereby changing clearances in the two opposed rotodynamic pumpingstages, affecting relative performance to balance the inlet pressures.In an alternate embodiment, external electronic control is employed tocontrol the position of the rotating assembly via an electromotiveforce, such as a solenoid-type element. The pump configurations of thepresent invention may also be applied to other fluid handlingapplications where inlet pressure balancing is desired.

The present invention relates to a blood pump that includes a housing, astator supported in the housing, and a rotor assembly. The rotorassembly includes a rotor supported in the housing for rotation relativeto the stator about an axis. The rotor assembly also includes a firstimpeller operatively coupled to a first axial end of the rotor forrotation with the rotor about the axis. The rotor assembly furtherincludes a second impeller operatively coupled to a second axial end ofthe rotor, opposite the first axial end, for rotation with the rotorabout the axis. The rotor assembly is movable along the axis relative tothe housing to adjust hydraulic performance characteristics of the pump.

The present invention also relates to a blood pump that includes a motorthat includes a stator and a rotor rotatable about an axis relative tothe stator. A first pump stage includes a first pump housing and a firstimpeller rotatable with the rotor about the axis in the first pumphousing. A second pump stage includes a second pump housing and a secondimpeller rotatable with the rotor about the axis in the second pumphousing. The blood pump is adapted to adjust the axial position of thefirst impeller in the first housing and the axial position of the secondimpeller in the second housing to adjust hydraulic performancecharacteristics of the first and second pump stages. Axial movement ofthe first and second stages is equal and opposite.

The present invention also relates to a blood pump that includes a motorcomprising a stator and a rotor rotatable about an axis relative to thestator. The blood pump also includes a first pump stage comprising afirst pump housing and a first impeller rotatable with the rotor aboutthe axis in the first pump housing. The blood pump further includes asecond pump stage comprising a second pump housing and a second impellerrotatable with the rotor about the axis in the second pump housing. Thefirst pump stage is configured to have a pressure rise that decreasessharply with increasing flow; the first pump stage flow thus beingprimarily a function of pump speed and impeller position. The secondpump stage is configured to have a pressure rise that is primarily afunction of pump speed and impeller position and substantiallyindependent of flow.

The present invention also relates to a pump including a housing thatdefines first and second pump housings. A rotor is supported in thehousing and rotatable about an axis. The rotor includes a first impellerdisposed in the first pump housing and a second impeller disposed in thesecond pump housing. The pump is configured such that inlet pressuresacting on the first impeller move the rotor relative to the housing in afirst direction along the axis and inlet pressures acting on the secondimpeller move the rotor relative to the housing in a second directionalong the axis opposite the first direction.

The present invention also relates to a pump including a housingincluding a pumping chamber and a rotor supported in the housing androtatable about an axis. The rotor includes an impeller at leastpartially disposed in the pumping chamber. The rotor is movable relativeto the housing in an axial direction parallel to the axis. The pump isconfigured such that axial movement of the rotor causes the impeller tomove axially between the pumping chamber and an adjacent chamber toalter the hydraulic performance of the pump.

The present invention also relates to a pump with a motor that includesa stator and a rotor. The stator is energizable to impart the rotor torotate about an axis. The motor is configured to permit the rotor tomove axially relative to the stator during operation of the pump. Afirst pumping stage includes a first pump housing and a first impellerpositioned in the first pump housing. The first impeller is connected toa first end of the rotor and is rotatable with the rotor about the axis.

The first pump housing and first impeller are configured to adjusthydraulic performance characteristics of the first pumping stagedepending on the axial position of the first impeller in the first pumphousing. A second pumping stage includes a second pump housing and asecond impeller positioned in the second pump housing. The secondimpeller is connected to a second end of the rotor and is rotatable withthe rotor about the axis. The second pump housing and second impellerare configured to adjust hydraulic performance characteristics of thesecond pumping stage depending on the axial position of the firstimpeller in the first pump housing. The first pumping stage isconfigured to urge the rotor in a first axial direction relative to thestator in response to inlet pressures acting on the first impeller, Thesecond pumping stage is configured to urge the rotor in a second axialdirection relative to the stator opposite the first axial direction inresponse to inlet pressures acting on the second impeller.

The present invention further relates to a total artificial heart pumpthat includes a left pump stage with an inlet for receiving left atrialblood flow and an outlet for discharging systemic blood flow via theaorta. The pump also includes a right pump stage with an inlet forreceiving right atrial blood flow and an outlet for dischargingpulmonary blood flow via the pulmonary artery. A motor includes a statorand a rotor for rotating a left impeller of the left pump stage and aright impeller of the right pump stage. The motor is configured topermit the rotor to move axially relative to the stator during operationof the pump. The pump is adapted such that differentials in left andright atrial pressures adjust the axial position of the rotor whichadjusts the relative hydraulic performance characteristics of the leftand right pump stages to balance the left and right atrial pressures andbalance the systemic and pulmonary discharge blood flows.

The present invention additionally relates to a pump that includes ahousing, a stator supported in the housing, and a rotor assemblyincluding a rotor supported in the housing for rotation relative to thestator about an axis. The stator includes a stator core, a firstlamination wound around an axial portion of the stator core, and asecond lamination wound around a second axial portion of the statorcore. The first and second laminations are spaced from each other alongthe length of the stator core. The rotor includes a rotor core, a firstmagnet assembly that extends around an axial portion of the rotor core,and a second magnet assembly that extends around a second axial portionof the rotor core. The first and second magnet assemblies are spacedfrom each other along the length of the rotor.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present invention will becomeapparent to those skilled in the art to which the present inventionrelates upon reading the following description with reference to theaccompanying drawings, in which:

FIG. 1 is a perspective view of a blood pump according to a firstembodiment of the present invention;

FIG. 2 is a sectional view of the blood pump taken generally along line2-2 in FIG. 1;

FIG. 3 is an exploded view of the blood pump of FIG. 1;

FIGS. 4 and 5 are plan views of portions of the blood pump of FIG. 1;

FIG. 6 is a sectional view illustrating a blood pump according to asecond embodiment of the present invention;

FIG. 7 is a sectional view illustrating a blood pump according to athird embodiment of the present invention;

FIG. 8 is a graph illustrating performance characteristics of the bloodpump of FIG. 7;

FIG. 9 is a perspective view of a blood pump according to a fourthembodiment of the present invention;

FIG. 10 is a front view of the blood pump of FIG. 9;

FIG. 11 is a perspective view of a portion of the blood pump of FIG. 9;

FIG. 12 is a sectional view of the blood pump taken generally along line12-12 in FIG. 9;

FIG. 13 is a graph illustrating characteristics of the blood pump ofFIG. 9;

FIGS. 14-16 are sectional views illustrating a blood pump according to afifth embodiment of the present invention;

FIG. 17 is a graph illustrating hydraulic performance characteristics ofthe blood pump of FIGS. 14-16;

FIG. 18 is a graph illustrating hydraulic performance characteristics ofthe blood pump of FIG. 12;

FIG. 19 is a graph illustrating hydraulic performance characteristics ofthe blood pump of FIG. 2; and

FIG. 20 is a sectional view illustrating a sixth embodiment of thepresent invention.

DESCRIPTION OF EMBODIMENTS

The present invention relates to a blood pump. FIG. 1 illustrates ablood pump 10 according to a first embodiment of the present invention.According to the present invention, the blood pump 10 is a totalartificial heart (TAH) device capable of replacing a failing or damagedhuman heart. Those skilled in the art, however, will appreciate that theblood pump 10 could be suitable for non-TAH implementations, such asbiventricular support. Those skilled in the art will also appreciatethat the pump may be suited for purposes other than pumping blood, suchas any implementation in which a dual or two stage fluid handling pumpwith pressure balancing features is desired. In the illustratedembodiments, the blood pump 10 is a two-stage centrifugal pump, which isdescribed below in further detail. The blood pump 10 could, however, bea rotodynamic pump of any desired configuration.

Referring to FIGS. 1-3, the blood pump 10 includes a stator assembly 20,a rotor assembly 30, a left pump housing 40, and a right pump housing50. In an assembled condition of the blood pump 10 (FIGS. 1 and 3), therotor assembly 30 is supported by the stator assembly 20 for rotationabout an axis 12. The pump housings 40 and 50 are fixed to the statorassembly 20 to enclose the rotor assembly 30. The rotor assembly 30includes a motor rotor 32, a first or left impeller 34, and a second orright impeller 36.

The motor rotor 32 includes a core 60 (FIG. 2) upon which a ring-shapedpermanent magnet 62 is mounted. A low density magnetically permeablefill material 64 may be used to support the magnet 62 on the motor rotor32, thereby allowing a neutral buoyancy rotating assembly, andinsensitivity to pump assembly attitude. The left and right impellers 34and 36 are secured to the core 60 by known means, such as adhesives ormechanical fasteners. Alternatively, the impellers 34 and 36 could beformed (e.g., molded) as a single piece of material with the core 60.

The stator assembly 20 includes a stator housing 22 that supports amotor stator 24. The motor stator 24 includes a stator core and motorwindings, illustrated schematically at 26 and 28, respectively in FIG.2. The motor windings 28 are electrically connected to three controlwires 70 of a control cable 72 that enters the stator housing 22 througha conduit 74 and is sealed by a potting material 76.

The blood pump 10, when assembled, includes a centrifugal first or leftpumping stage or pump 42. The left pump 42 includes the left impeller 34and a left pump chamber 44 in which the left impeller is disposed. Theleft pump chamber 44 is defined, at least partially, by the left pumphousing 40 and the stator assembly 20. The left pump 42 also includes aleft pump inlet 46 and a left pump outlet 48 that, in the illustratedembodiment, are formed as integral portions of the left pump housing 40.The left pump housing 40 includes an inlet surface 90 that helps definean inlet portion 92 of the left pump chamber 44 in fluid communicationwith the inlet 46. The left pump housing 40 also includes a volutesurface 94 that helps define a volute portion 96 of the left pumpchamber 44 in fluid communication with the outlet 48.

The blood pump 10, when assembled, also includes a centrifugal second orright pumping stage or pump 52. The right pump 52 includes the rightimpeller 36 and a right pump chamber 54 in which the right impeller isdisposed. The right pump chamber 54 is defined, at least partially, bythe right pump housing 50 and the stator assembly 20. The right pump 52also includes a right pump inlet 56 and a right pump outlet 58 that, inthe illustrated embodiment, are formed as integral portions of the rightpump housing 50. The right pump housing 50 includes an inlet surface 100that helps define an inlet portion 102 of the right pump chamber 54 influid communication with the inlet 56. The right pump housing 50 alsoincludes a volute surface 104 that helps define a volute portion 106 ofthe right pump chamber 54 in fluid communication with the outlet 58.

The motor rotor 32 and motor stator 24 help define a motor 80 of theblood pump 10 that drives the left and right pumps 42 and 52. The motor80 may be any type of electric motor suited to drive the pumps 42 and 52and deliver the desired performance characteristics. For example, in theillustrated embodiment, the motor 80 may have a single phase ormulti-phase brushless, sensorless DC motor configuration. A motorcontroller 82 is operative to excite the phase windings 28 of the motor80 via the cable 72 to achieve desired performance of the motor portion,such as motor speed or current. For example, the motor controller 82apply pulse width modulated voltage to the motor phases in order toachieve the desired motor/pump performance.

During operation of the blood pump 10, the rotor assembly 30 rotatesabout the axis 12 relative to the stator assembly 20. The rotor assembly30 is supported or rides on a hydrodynamic or fluid film bearing formedby the pumped fluid, i.e., blood. Alternatively, the blood pump 10 couldinclude other types of bearing features, such as mechanical bearings orbearing surfaces formed from or coated with low friction materials, forfacilitating rotation of the rotor assembly 30. As a furtheralternative, the rotor assembly 30 could be magnetically suspended.

The materials used to construct the blood pump 10 may be formed frommaterials conducive to blood pumping implementations. For example,portions of the blood pump 10 that are exposed to blood flow during use,such as the impellers 34 and 36 and pump housings 40 and 50, may beformed from, coated, or encased in a biocompatible material, such asstainless steel, titanium, ceramics, polymeric materials, compositematerials, or a combination of these materials. Surfaces or portions ofthe blood pump 10 that may contact each other during use, such as theleft impeller 34 and pump housing 40 or the right impeller 36 and pumphousing 50, may also be formed or coated with low friction materials,such as a fluorocarbon polymer coatings, diamond-like carbon coatings,ceramics, titanium, and diamond coated titanium.

Referring to FIG. 1, arrows are used to illustrate the blood pump 10 ina total artificial heart (TAH) implementation in which the pump takesover the function of a patient's heart (not shown). In thisconfiguration, the left pump inlet 46 is connected with the left atrium,the left pump outlet 48 is connected to the aorta, the right pump inlet56 is connected to the right atrium, and the right pump outlet 58 isconnected to the pulmonary artery. In operation, the left pump 42delivers oxygenated blood to the aorta from the left atrium and theright pump 52 delivers deoxygenated blood to the pulmonary artery fromthe right atrium.

Those skilled in the art will appreciate that, in a TAH scenario, it isimportant to balance pulmonary and systemic arterial blood flows andatrial pressures. For example, if the right pump 52 delivers blood at ahigher flow rate than the left pump 42, blood may accumulate in thelungs and can lead to congestive heart failure. For example, if the leftpump 42 delivers blood at a higher flow rate than the right pump 52,blood may accumulate in the liver and can lead to liver failure. Thegoal for the blood pump 10 is thus to balance pulmonary and systemicarterial blood flows and atrial pressures. According to the presentinvention, the blood pump 10 balances systemic and pulmonary atrialpressures and arterial flow rates by adjusting the geometry orconfiguration of the left (systemic) pump 42 and right (pulmonary) pump52.

According to the present invention, the blood pump 10 is configured witha clearance that permits axial movement of the rotor assembly 30relative to the stator assembly 20. Referring to FIG. 2, the rotorassembly 30 is positioned about midpoint in this axial clearance,leaving an axial back clearance between the left impeller 34 and thestator housing 22, identified generally at “A1 ,” and an axial backclearance between the right impeller 36 and the stator housing 22,identified generally at “A2.” With the configuration shown in FIG. 2, ithas been found that maximum left pump 42 performance occurs when A1 isminimum, and maximum right pump 52 performance occurs when A2 isminimum. During operation of the blood pump 10, the rotor assembly 30can move or shuttle axially relative to the stator assembly 20 due tohydrodynamic pumping forces created by the left and right pumps 42 and52. The rotor assembly 30 can move axially between a left position, inwhich the left impeller 34 is positioned with A1 being maximum, and aright position, in which the right impeller 36 is positioned with A2being maximum.

When the rotor assembly 30 moves axially between the left and rightpositions, the configurations or geometries of the left and right pumps42 and 52 are altered. As the axial position of the left impeller 34changes, the clearance A1 between the left impeller and the statorassembly 22 changes, which alters the configuration and geometry of theleft pump 42 and left pump chamber 44. Similarly, as the axial positionof the right impeller 36 changes, the clearance A2 between the rightimpeller and the stator assembly 22 changes, which alters theconfiguration and geometry of the right pump chamber 54 and theconfiguration or geometry of the right pump 52.

As the clearances A1 and A2 increase, the first and second pumps 42 and52 decrease in hydraulic output. Thus, for a given pump speed, as theimpellers 34 and 36 move toward the stator assembly 22 (i.e., reducingtheir respective clearances A1 and A2), the pumps 42 and 52 increase inpressure and flow accordingly. Conversely, as the impellers 34 and 36move away from the stator assembly 22 (i.e., increasing their respectiveclearances A1 and A2), the pumps 42 and 52 decrease in pressure and flowaccordingly.

It will thus be appreciated that, for the single motor, two-stageconfiguration of the blood pump 10 of the present invention, axialmovement of the rotor assembly 30 that produces increased pressure andflow at the left pump stage 42 will also produce a decrease in pressureand flow at the right pump stage 52. Similarly, axial movement of therotor assembly 30 that produces increased pressure and flow at the rightpump stage 52 will also produce a decrease in pressure and flow at theleft pump stage 42. From this, it follows that, for any given speed ofthe blood pump 10, the pressures and flows of the left and right pumpstages 42 and 52 can be balanced if the axial position of the rotorassembly 30 relative to the stator assembly 20 is adjusted to the properposition.

Based on this principle, using the blood pump 10, systemic and pulmonarypressure and flow characteristics can be controlled through adjustingthe axial position of the rotor assembly 30. According to the presentinvention, the axial position of the of the rotor assembly 30 can becontrolled passively or actively. The embodiment of FIGS. 1-5illustrates a configuration of the blood pump 10 in which passivecontrol is used to adjust the axial position of the rotor assembly 30and, thus, the geometry or configuration of the left and right pumps 42and 52.

In the passive control configuration of the blood pump 10, the axialposition of the rotor assembly 30 is controlled passively or inherentlythrough hydraulic forces created by the left and right pumps 42 and 52during operation. According to the present invention, the configurationsof the left and right impellers 34 and 36 are chosen to help producethis operation. Referring to FIG. 4, the first impeller 34 includes aback plate 110 and a plurality of vanes 112 that extend radially fromthe back plate. In the embodiment of FIG. 4, the vanes 112 include firstor primary vanes 114 and second or splitter vanes 116, the splittervanes being shorter than the primary vanes. In the embodimentillustrated in FIG. 5, the vanes 112 are configured with a low incidenceinlet and a radial discharge.

Referring to FIG. 5, the second impeller 36 includes a back plate 120and a plurality of vanes 122 that extend radially from the back plate.In the embodiment of FIG. 5, the vanes 122 include first or primaryvanes 124 and second or splitter vanes 126, the second vanes beingshorter than the first vanes. In the embodiment illustrated in FIG. 5,the vanes 122 are configured with a low incidence inlet and a radialdischarge.

The back plates 110 and 120 of the first and second impellers 34 and 36are about equal in size or diameter. The vanes 112 of the first impeller34 are longer than the corresponding vanes 122 of the second impeller36. The configurations of the first and second impellers 34 and 36 inthe embodiment of FIGS. 1-4 illustrate one example impellerconfiguration. Those skilled in the art will appreciate that theimpellers 34 and 36 could have alternative configurations.

The back plates 110 and 120 have reduced diameters such that the vanes112 and 122, respectively, extend radially beyond their outer edges. Theback plates 110 and 120 are directly facing the left and right pumpinlets 46 and 56, respectively. Therefore, fluid pressures acting on theback plates 110 and 120 are primarily inlet pressures and thus exertforces on the rotor assembly 30 that are primarily axial, i.e., parallelto the axis 12. Outlet pressures produced by the blood pump 10 aregenerated primarily at the end portions of the vanes 112 and 122 thatare positioned radially beyond the outer diameter of the back plates 110and 120.

The blood pump 10 of the illustrated embodiment has a configuration thatdiffers from that of a conventional centrifugal pump design in two basicways. First, the blood pump 10 utilizes an open-vaned impeller with anunusually high axial clearance having non-symmetrical front and backaxial clearances (see FIGS. 2 and 3). Second, the radial vanes extendinto the volute section in a manner typical for a peripheral (orregenerative) pump. This extension creates a back-of-vane clearance forpassive performance modulation. Also, the rotor magnet 62, being shorterthan the stator core 26, allows for a controlled amount of free axialmovement of the rotating assembly 30.

It has been found that for constant system resistances, output flow andpump speed have a linear relationship. As a result, the controlalgorithm executed by the controller 82 adjusts pump speed to provide anominal systemic flow. Balanced systemic and pulmonary flows areachieved by adjusting of the axial position of the rotor assembly 30.According to the first embodiment of the invention, the axialadjustments of the rotor assembly 30 occur inherently or automaticallyas a result of the configurations of the left and right impellers 34 and36 and due to hydraulic pressures.

Because the axial hydrodynamic forces acting on the back plate portions110 and 120 of the impellers 34 and 36 are primarily those created bypump inlet pressures, the axial position of the rotor assembly 30adjusts in response to pressure differentials between the left and rightinlet portions 92 and 102. As the axial position of the rotor assembly30 adjusts, the geometry and hydraulic performance of the left and rightpumps 42 and 52 changes, as described above. This produces acorresponding change or adjustment in the outlet flows and pressures ofthe left and right pumps 42 and 52, trading pressure and flowperformance between the two pumps. The blood pump 10 is thus configuredwith a self-adjusting rotor assembly 30 that helps balance pulmonary andsystemic flows, as well as atrial pressures, through incremental changesthe hydraulic performance of the left and right pumps 42 and 52.

When operating in high clearance, minimum pump performance occurs whenthe pumping vanes are centered in the axial clearance (front and backclearances equal). Therefore, performance can be modulated by moving theimpellers 34 and 36 in either axial direction. In the self-balancingconfiguration of FIG. 2, maximum performance for the left pump 42 occurswhen back clearance A1 is minimum, while maximum performance for theright pump 52 occurs when back clearance A2 is minimum. The passivecontrol implemented in the embodiment of FIG. 2 modulates performance byadjusting the back clearances A1 and A2. The advantage of using the back(inside) edges to modulate performance is that hydraulic forcesoperating on the rotating assembly can enforce the correct direction ofaxial movement for passive control, thereby eliminating the need for anactive axial control system.

During operation of the blood pump 10 as TAH, pump speed can bemodulated at normal pulse rates to create pulsatile flow and pressure,simulating normal hemodynamics in the patient. For example, it was foundthat a ±30% speed modulation enforces a highly pulsatile condition.Further, the speed wave form can be adjusted to tailor thecharacteristics of the systemic pressure pulses to mimic the amplitudeand systolic/diastolic timing desired clinically.

Advantageously, since flow is directly related to current and speed, thecurrent wave form can be analyzed to determine any interruptions in flowduring each control cycle. This may, for example, help detect collapseof the left or right atria, in which case an incremental decrease inaverage speed or magnitude of the speed pulsation may be triggeredautomatically. Also, based on the motor current response to the speedand duty cycle, the patient's pulmonary and systemic pressures andvascular resistances can be estimated by calculation, allowing thesystem to be used as a continuous patient monitor.

A second embodiment of the present invention is illustrated in FIG. 6.The second embodiment of the invention is similar to the firstembodiment of the invention illustrated in FIGS. 1-5. Referring to FIG.6, the blood pump 200 has a two-stage centrifugal pump configurationsimilar to that of FIGS. 1-5. The blood pump 200 may thus be configuredfor use as a total artificial heart (TAH) device. The blood pump 200could, however, be suitable for non-TAH implementations, such asbiventricular support or any implementation in which a dual or two stagefluid handling pump with pressure balancing features is desired.

Referring to FIG. 6, the blood pump 200 includes a stator assembly 220,a rotor assembly 230, a left pump housing 240, and a right pump housing250. In the assembled condition, the rotor assembly 230 is supported bythe stator assembly 220 for rotation about an axis 212. The pumphousings 240 and 250 are fixed to the stator assembly 220 to enclose therotor assembly 230. The rotor assembly 230 includes a motor rotor 232, afirst or left impeller 234, and a second or right impeller 236.

The motor rotor 232 includes a core 260 upon which a ring-shapedpermanent motor magnet 262 is mounted. A fill material 264, such as alow density magnetically permeable material, may be used to help supportthe magnet 262 on the motor rotor 232. The left and right impellers 234and 236 are secured to the core 260 by known means, such as adhesives ormechanical fasteners. Alternatively, the impellers 234 and 236 could beformed (e.g., molded) as a single piece of material with the core 260.

The stator assembly 220 includes a stator housing 222 that supports amotor stator 224. The motor stator 224 includes a stator core and motorwindings, illustrated schematically at 226 and 228, respectively in FIG.6. The motor windings 228 are electrically connected to control wires270 of a control cable 272 that enters the stator housing 222 through aconduit 274 and is sealed by a potting material 276.

The blood pump 200, when assembled, includes a centrifugal first or leftpumping stage or pump 242. The left pump 242 includes the left impeller234 and a left pump chamber 244 in which the left impeller is disposed.The left pump chamber 244 is defined, at least partially, by the leftpump housing 240 and the stator assembly 220. The left pump 242 alsoincludes a left pump inlet 246 and a left pump outlet 248 that, in theillustrated embodiment, are formed as integral portions of the left pumphousing 240. The left pump housing 240 includes an inlet surface 290that helps define an inlet portion 292 of the left pump chamber 244 influid communication with the inlet 246. The left pump housing 240 alsoincludes a volute surface 294 that helps define a volute portion 296 ofthe left pump chamber 244 in fluid communication with the outlet 248.

The blood pump 200, when assembled, also includes a centrifugal secondor right pumping stage or pump 252. The right pump 252 includes theright impeller 236 and a right pump chamber 254 in which the rightimpeller is disposed. The right pump chamber 254 is defined, at leastpartially, by the right pump housing 250 and the stator assembly 220.The right pump 252 also includes a right pump inlet 256 and a right pumpoutlet 258 that, in the illustrated embodiment, are formed as integralportions of the right pump housing 250. The right pump housing 250includes an inlet surface 300 that helps define an inlet portion 302 ofthe right pump chamber 254 in fluid communication with the inlet 256.The right pump housing 250 also includes a volute surface 304 that helpsdefine a volute portion 306 of the right pump chamber 254 in fluidcommunication with the outlet 258.

The motor rotor 232 and motor stator 224 help define a motor 280 of theblood pump 200 that drives the left and right pumps 242 and 252. Themotor 280 may be any type of electric motor suited to drive the pumps242 and 252 and deliver the desired performance characteristics. Forexample, in the illustrated embodiment, the motor 280 may have amulti-phase brushless DC motor configuration. A motor controller 282 isoperative to excite the phase windings 228 of the motor 280 via thecable 272 to achieve desired performance of the motor portion, such asmotor speed or current. For example, the motor controller 282 applypulse width modulated voltage to the motor phases in order to achievethe desired the desired motor/pump performance.

During operation of the blood pump 200, the rotor assembly 230 rotatesabout the axis 212 relative to the stator assembly 220. The rotorassembly 230 is supported or rides on a hydrodynamic or fluid filmbearing formed by the pumped fluid, i.e., blood. Alternatively, theblood pump 200 could include other types of bearing features, such asmechanical bearings or bearing surfaces formed from or coated with lowfriction materials, for facilitating rotation of the rotor assembly 230.As a further alternative, the rotor assembly 230 could be magneticallysuspended.

The materials used to construct the blood pump 200 may be formed frommaterials conducive to blood pumping implementations. For example,portions of the blood pump 200 that are exposed to blood flow duringuse, such as the impellers 234 and 236 and pump housings 240 and 250,may be formed from, coated, or encased in a biocompatible material, suchas stainless steel, titanium, ceramics, polymeric materials, compositematerials, or a combination of these materials. Surfaces or portions ofthe blood pump 200 that may contact each other during use, such as theleft impeller 234 and pump housing 240 or the right impeller 236 andpump housing 250, may also be formed or coated with low frictionmaterials, such as fluorocarbon polymer coatings, diamond-like carboncoatings, ceramics, titanium, and diamond coated titanium.

In FIG. 6, arrows are used to illustrate the blood pump 200 in a totalartificial heart (TAH) implementation in which the pump takes over thefunction of a patient's heart (not shown). In this configuration, theleft pump inlet 246 is connected with the left atrium, the left pumpoutlet 248 is connected to the aorta, the right pump inlet 256 isconnected to the right atrium, and the right pump outlet 258 isconnected to the pulmonary artery. In operation, the left pump 242delivers oxygenated blood to the aorta from the left atrium and theright pump 252 delivers deoxygenated blood to the pulmonary artery fromthe right atrium.

According to the present invention, the blood pump 200 balances systemicand pulmonary pressures and flow rates by adjusting the geometry orconfiguration of the left (systemic) pump 242 and right (pulmonary) pump252. The blood pump 200 is configured with a clearance that permitsaxial movement of the rotor assembly 230 relative to the stator assembly220. In FIG. 6, the rotor assembly 230 is positioned about midpoint inthis axial clearance, leaving an axial clearance between the leftimpeller 234 and the left pump housing 240, identified generally at“B1,” and an axial clearance between the right impeller 236 and theright pump housing 250, identified generally at “B2.” During operationof the blood pump 200, the rotor assembly 230 can move or shuttleaxially relative to the stator assembly 220 due to electromotive forceof an actuator 350, such as an electric solenoid, that is connected tothe controller 282 via the cable 272. The rotor assembly 230 can moveaxially between a left position, in which the left impeller 234 ispositioned adjacent or engaging the left pump housing 240, and a rightposition, in which the right impeller 236 is positioned adjacent to theright pump housing 250.

When the rotor assembly 230 moves axially between the left and rightpositions, the configurations or geometries of the left and right pumps242 and 252 are altered. As the axial position of the left impeller 234changes, the clearance B1 between the left impeller and the left pumphousing 240 changes, which alters the volume of the left pump chamber244 and the configuration or geometry of the left pump 242. Similarly,as the axial position of the right impeller 236 changes, the clearanceB2 between the right impeller and the right pump housing 250 changes,which alters the volume of the right pump chamber 254 and theconfiguration or geometry of the right pump 252.

As the clearances B1 and B2 increase, the first and second pumps 242 and252 reduce hydraulic output. Thus, for a given pump speed, as theimpellers 234 and 236 move toward their respective pump housings 240 and250 (i.e., reducing their respective clearances B1 and B2), the pumps242 and 252 increase pressure and flow increase accordingly. Conversely,as the impellers 234 and 236 move away from their respective pumphousings 240 and 250 (i.e., increasing their respective clearances B1and B2), the pumps 242 and 252 decrease pressure and flow decreaseaccordingly.

It will thus be appreciated that, for the single motor, two-stageconfiguration of the blood pump 200 of the present invention, axialmovement of the rotor assembly 230 that produces increased pressure andflow at the left pump stage 242 will also produce a decrease in pressureand flow at the right pump stage 252. Similarly, axial movement of therotor assembly 230 that produces increased pressure and flow at theright pump stage 252 will also produce a decrease in pressure and flowat the left pump stage 242. From this, it follows that, for any givenspeed of the blood pump 200, the pressures and flows of the left andright pump stages 242 and 252 can be balanced if the axial position ofthe rotor assembly 230 relative to the stator assembly 220 is adjustedto the proper position.

Based on this principle, using the blood pump 200, systemic andpulmonary pressure and flow characteristics can be controlled throughadjusting the axial position of the rotor assembly 230. According to thesecond embodiment of the present invention, the blood pump 200 isconfigured for active control of the axial position of the of the rotorassembly 230 and, thus, the geometry or configuration of the left andright pumps 242 and 252.

It has been found that, for constant system resistances, output flow andpump speed have a linear relationship. It has also been found that, fora given pump speed, there is an electrical power level, obtained byadjusting the axial position of the rotor assembly 230, that correspondswith balanced flows at the left pump 242 and right pump 252. As aresult, the control algorithm executed by the controller 282 adjustspump speed to provide a nominal systemic flow, while balanced systemicand pulmonary flows are achieved by adjusting of the axial position ofthe rotor assembly 230. According to the second embodiment of theinvention, the axial adjustments of the rotor assembly 230 relative tothe stator assembly 220 are achieved through the use of anelectro-mechanical actuator 350, such as a solenoid, that is connectedto the controller 282 via the cable 272. The solenoid 350 is actuatableto one of two positions: a first or left position and a second or rightposition. In the left position, the solenoid 350 causes the axialposition of the rotor assembly 230 to shift to a first or left position,in which the left impeller 234 is positioned adjacent or near the inletsurface 290 of the left pump housing 240, effectively increasing thehydraulic output of the left pump stage 242 and decreasing the hydraulicoutput of the right pump stage 252, as described above. In the rightposition, the solenoid 350 causes the axial position of the rotorassembly 230 to shift to a second or right position, in which the rightimpeller 236 is positioned adjacent or near the inlet surface 300 of theright pump housing 250, effectively increasing the hydraulic output ofthe right pump stage 252 and decreasing the hydraulic output of the leftpump stage 252, as described above.

The solenoid 350 may be configured to place the rotor assembly 230 inthe left and right positions in a variety of manners. For example, thesolenoid 350 may be a latching solenoid. In this configuration, thesolenoid 350 may include two separate coils 352, one for selecting theleft position and one for selecting the right position, fixed to thestator assembly 220 and an armature 354, such as one or more magnets,fixed to the rotor assembly 230. In this latching configuration, thesolenoid 350 includes a magnetic latching mechanism that maintains therotor assembly 230 in the selected position without constant applicationof power to the solenoid. In operation, the coils 352 may be energizedby a short current pulse of sufficient magnitude and duration to movethe armature 354, and thus the rotor assembly 230, to the desiredleft/right position. At this point, the latching mechanism is actuatedand maintains the rotor 230 at the desired position. When the oppositecoil is energized, the latching mechanism releases the rotor assembly230 to move to the opposite position under the pull of the coil 352 onthe armature 354. The mechanism then latches magnetically, thusmaintaining the axial position of the rotor assembly 230 when the coil352 is de-energized.

In an alternative configuration, the solenoid 350 may be a ratcheting ortoggle-type latching solenoid configured for pulse-left/pulse-rightoperation. In this configuration, the solenoid 350 may include a singlecoil and latch mechanism that, when the coil is energized, latches therotor assembly alternately in the left and right positions. Thus, duringoperation, if the rotor assembly is in the right position, the nextenergy pulse will place the rotor assembly in the left position. Thenext energy pulse will then place the rotor assembly in the rightposition, and so on.

In another alternative configuration, the solenoid 350 may be anon-latching, continuous current solenoid. In this configuration, thesolenoid may include a single coil for moving an armature that is springbiased to one of the left and right positions. When the coil isde-energized, the spring maintains the armature and thus the rotor, atone of the left and right positions. When the coil is energized, thearmature and rotor are moved against the spring bias to the oppositeposition. The armature and rotor are maintained at this position untilthe coil is de-energized, at which time the spring moves the armatureand rotor back to the original position.

In operation of the blood pump 200, motor speed is modulated at normalpulse rates to create pulsatile flow and pressure. Balanced systemic andpulmonary flow and atrial pressure balance are achieved through activeadjustments of the axial position of the rotor assembly 230 via thesolenoid 350 to adjust the hydraulic performance of the left and rightpumps 242 and 252. These balanced flows and pressures are achieved bysplitting the control cycle (e.g., 10 seconds) between the left andright positions. Left and right flow will be estimated from the speed,power consumption, and the change in power consumption as the rotorassembly 230 toggles between the left and right axial positions.

In operation, the axial position of the rotor assembly 230 is toggledback and forth between the left and right positions during the controlcycle (e.g., ten seconds) of the pump 200. As the axial position of therotor assembly 230 toggles, the geometry and hydraulic performance ofthe left and right pumps 242 and 252 changes, as described above. Thisproduces a corresponding net change or adjustment in the outlet flowsand pressures of the left and right pumps 242 and 252, increasing theoutlet flow and pressure on one side of the pump and decreasing theoutlet flow and pressure at the opposing side of the pump. The bloodpump 200 and the controller 282 are thus configured to balance pulmonaryand systemic flows, as well as atrial pressures, through incrementalchanges in the hydraulic performance of the left and right pumps 242 and252.

The active control embodiment of the blood pump 200 of FIG. 6 uses frontvane clearance to modulate performance. This has two potentialadvantages. First, right/left performance bias can be controlledexternally at the expense of more complexity. Second, the total axialclearance is less, allowing better pump efficiency. Also, the rotormagnet 262 is shorter than the stator core 226 to allow a controlledamount of free axial movement of the rotating assembly 230.

During operation of the blood pump 200, left and right atrial pressuresequilibrate to within several mmHg. As the flow approaches equilibrium,trending in the current draw of the pump 200 indicates the direction ofadjustment for fine-tuning the duty cycle. Also, pump speed can bemodulated at normal pulse rates to create pulsatile flow and pressureand stable hemodynamics in the patient. For example, it was found that a±30% speed modulation enforces a highly pulsatile condition. Further,the speed wave form can be adjusted to tailor the characteristics of thesystemic pressure pulses to mimic the amplitude and systolic/diastolictiming desired clinically.

Advantageously, since flow is approximately related to current andspeed, the current wave form can be analyzed to determine anyinterruptions in flow during each control cycle. This may, for example,help detect collapse of the left or right atria, in which case anincremental decrease in average speed or magnitude of the speedpulsation may be triggered automatically. Also, based on the speed andduty cycle, the patient's pulmonary and systemic pressures and vascularresistances can be estimated by calculation, allowing the system to beused as a continuous patient monitor.

A blood pump 400 according to a third embodiment of the presentinvention is illustrated in FIG. 7. The blood pump 400 of FIG. 7 has aconfiguration that is similar to the embodiment of FIG. 6, except thatthe embodiment of FIG. 7 includes a rotor assembly 410 that does notmove axially to alter the pump geometry during operation. In thisconfiguration, the rotor magnet 420 is the same length or longer thanthe stator core 422, which magnetically constrains the axial position ofthe rotor assembly 410.

The blood pump 400 of FIG. 7 may be particularly well-suited for use asa ventricular assist device (VAD), such as a bi-ventricular assistdevice (BiVAD) that combines right ventricular assist device (RVAD) andleft ventricular assist device (LVAD) functions in a single pump. Withan RVAD, the total pulmonary artery flow is shared between the VAD andnative ventricle, so precise right/left pump control is not as criticalas for a total artificial heart. It has been found that performancecharacteristics can be crafted into the pumping element design, whichcan allow a degree of completely passive regulation of a BiVAD system.In this embodiment, the configurations and geometries of the left pump442 (LVAD) and right pump 452 (RVAD) may be designed to have pressureversus flow characteristics similar to those shown in FIG. 8. As shownin FIG. 8, the left pump 442 has a pressure rise that decreases sharplywith increasing flow, causing the left flow to be primarily a functionof speed. The right pump 452 has a characteristic pressure rise that isa function of speed, and relatively independent of flow. In this way,the left pump 442 acts as a flow regulator for systemic flow, while theright pump 452 acts as a differential pressure regulator for moderateunloading the right ventricle.

A blood pump 500 according to a fourth embodiment of the presentinvention is illustrated in FIGS. 9-12. The blood pump 500 of FIGS. 9-12has a two-stage or dual centrifugal pump configuration that is similarto the embodiments of FIGS. 1-5 and 7. The blood pump 500 may thus beconfigured for use as a total artificial heart (TAH) device. The bloodpump 500 could, however, be suitable for non-TAH implementations, suchas biventricular support or any implementation in which a dual or twostage fluid handling pump with pressure balancing features is desired.

Referring to FIGS. 9-11, the blood pump 500 includes a stator assembly520, a rotor assembly 530, a left pump housing 540, and a right pumphousing 550. In an assembled condition of the blood pump 500, the rotorassembly 530 is supported by the stator assembly 520 for rotation aboutan axis 512. The pump housings 540 and 550 are fixed to the statorassembly 520 to enclose the rotor assembly 530. The rotor assembly 530includes a motor rotor 532, a first or left impeller 534, and a secondor right impeller 536.

The motor rotor 532 includes a core 560 (FIG. 12) surrounded orotherwise encased in a shell or casing 564 upon which a ring-shapedpermanent magnet 562 is mounted. The core 560 may be constructed of alow density magnetically permeable material, may be used to help supportthe magnet 562 on the motor rotor 532, thereby allowing a neutralbuoyancy rotating assembly and insensitivity to the attitude of the pumpassembly. The left and right impellers 534 and 536 may be secured to thecore 560 by known means, such as adhesives or mechanical fasteners, or,as shown in FIGS. 9-11, could be formed (e.g., molded) as a single pieceof material with the shell 564.

The stator assembly 520 includes a stator housing 522 that supports amotor stator 524. The motor stator 524 includes a stator core and motorwindings, illustrated schematically at 526 and 528, respectively in FIG.12. The motor windings 528 are electrically connected to control wires570 of a control cable 572 that enters the stator housing 522 through aconduit 574 and a strain relief material 576.

The blood pump 500, when assembled, includes a centrifugal first or leftpumping stage or pump 542. The left pump 542 includes the left impeller534 and a left pump chamber 544 in which the left impeller is disposed.The left pump chamber 544 is defined, at least partially, by the leftpump housing 540 and the stator assembly 520. The left pump 542 alsoincludes a left pump inlet 546 and a left pump outlet 548 that, in theillustrated embodiment, are formed as integral portions of the left pumphousing 540. The left pump housing 540 includes an inlet surface 590that helps define an inlet portion 592 of the left pump chamber 544 influid communication with the inlet 546. The left pump housing 540 alsoincludes a volute surface 594 that helps define a volute portion 596 ofthe left pump chamber 544 in fluid communication with the outlet 548.

The blood pump 500, when assembled, also includes a centrifugal secondor right pumping stage or pump 552. The right pump 552 includes theright impeller 536 and a right pump chamber 554 in which the rightimpeller is disposed. The right pump chamber 554 is defined, at leastpartially, by the right pump housing 550 and the stator assembly 520.The right pump 552 also includes a right pump inlet 556 and a right pumpoutlet 558 that, in the illustrated embodiment, are formed as integralportions of the right pump housing 550. The right pump housing 550includes an inlet surface 600 that helps define an inlet portion 602 ofthe right pump chamber 554 in fluid communication with the inlet 556.The right pump housing 550 also includes a volute surface 604 that helpsdefine a volute portion 606 of the right pump chamber 554 in fluidcommunication with the outlet 558. The right pump housing 550 furtherincludes a chamber 608 adjacent the volute portion 606 into which theright impeller 536 enters as the rotor assembly 530 moves axially to theright as viewed in FIG. 12. The right impeller 536 leaves the voluteportion 606 as it enters the chamber 608.

The motor rotor 532 and motor stator 524 help define a motor 580 of theblood pump 500 that drives the left and right pumps 542 and 552. Themotor 580 may be any type of electric motor suited to drive the pumps542 and 552 and deliver the desired performance characteristics. Forexample, in the illustrated embodiment, the motor 580 may have a singlephase or multi-phase brushless, sensorless DC motor configuration. Amotor controller (not shown) is operative to excite the phase windings528 of the motor 580 via the cable 572 to achieve desired performance ofthe motor portion, such as motor speed or current. For example, themotor controller may apply pulse width modulated voltage to the motorphases in order to achieve the desired motor/pump performance.

Referring to FIG. 11, the first impeller 534 includes a back plate 610and a plurality of vanes 612 that extend radially from the rotor 530.The vanes 612 include first or primary vanes 614 and second or splittervanes 616, the splitter vanes being shorter than the primary vanes. Inthe embodiment illustrated in FIGS. 9-12, there are two splitter vanes616 positioned between pairs of primary vanes 614. The vanes 612 areconfigured with a low incidence inlet and a radial discharge.

The second impeller 536 includes a back plate 620 and a plurality ofvanes 622 that extend radially along the end face of the rotor 530. Thevanes 622 include first or primary vanes 624 and second or splittervanes 626, the second vanes being shorter than the first vanes. In theembodiment illustrated in FIGS. 9-12, the primary vanes 624 and splittervanes 626 are arranged in an alternating fashion about the rotor 530.The vanes 622 are configured with a low incidence inlet and a radialdischarge.

The vanes 612 of the first impeller 534 are longer than thecorresponding vanes 622 of the second impeller 536. The configurationsof the first and second impellers 534 and 536 in the embodiment of FIGS.9-12 illustrate one example impeller configuration. Those skilled in theart will appreciate that the impellers 534 and 536 could havealternative configurations.

The back plates 610 and 620 are aligned axially with the left and rightpump inlets 546 and 556, respectively. Therefore, fluid pressures actingon the back plates 610 and 620 are primarily inlet pressures and thusexert forces on the rotor assembly 530 that are primarily axial, i.e.,parallel to the axis 512. Outlet pressures produced by the blood pump500 are generated primarily at the end portions of the vanes 612 and622. The vanes 612 of the first impeller 534 extend radially beyond theouter diameter of the back plate 610.

During operation of the blood pump 500, the rotor assembly 530 rotatesabout the axis 512 relative to the stator assembly 520. The rotorassembly 530 is supported or rides on a hydrodynamic or fluid filmbearing formed by the pumped fluid, i.e., blood. Alternatively, theblood pump 500 could include other types of bearing features, such asmechanical bearings or bearing surfaces formed from or coated with lowfriction materials, for facilitating rotation of the rotor assembly 530.As a further alternative, the rotor assembly 530 could be magneticallysuspended.

The materials used to construct the blood pump 500 may be formed frommaterials conducive to blood pumping implementations. For example,portions of the blood pump 500 that are exposed to blood flow duringuse, such as the impellers 534 and 536 and pump housings 540 and 550,may be formed from, coated, or encased in a biocompatible material, suchas stainless steel, titanium, ceramics, polymeric materials, compositematerials, or a combination of these materials. Surfaces or portions ofthe blood pump 500 that may contact each other during use, such as theleft impeller 534 and pump housing 540, the right impeller 536 and pumphousing 550, or the rotor casing 564, may also be formed or coated withlow friction materials, such as a fluorocarbon polymer coatings,diamond-like carbon coatings, ceramics, titanium, and diamond coatedtitanium.

Those skilled in the art will appreciate that, in a TAH scenario, it isimportant to balance pulmonary and systemic arterial blood flows andatrial pressures. For example, if the right pump 552 delivers blood at ahigher flow rate than the left pump 542, blood may accumulate in thelungs and can lead to congestive heart failure. As another example, ifthe left pump 542 delivers blood at a higher flow rate than the rightpump 552, blood may accumulate in the liver and can lead to liverfailure. The goal for the blood pump 500 is thus to balance pulmonaryand systemic arterial blood flows and atrial pressures. According to thepresent invention, the blood pump 500 balances systemic and pulmonaryatrial pressures and arterial flow rates by adjusting the geometry orconfiguration of the left (systemic) pump 542 and right (pulmonary) pump552.

According to the present invention, the blood pump 500 is configuredwith a clearance that permits axial movement of the rotor assembly 530relative to the stator assembly 520. Referring to FIG. 12, the rotorassembly 530 is positioned about midpoint in this axial clearance. Theblood pump 500 has an axial back clearance between the left impeller 534and the left pump housing 540 identified generally at “D1.” As shown inFIG. 12, D1 is the clearance between the vanes 612 of the left impeller534 and a back surface 578 of the left pump chamber 544, which may bedefined at least partially by the stator assembly 520, the left pumphousing 540, or both the stator assembly and the left pump housing.During operation of the pump 500, when the rotor assembly 530 movesaxially relative to the stator assembly 520, the left impeller 534 movesaxially within the left pump chamber 544.

The blood pump 500 has an axial front clearance between the rightimpeller 536 and the right pump housing 550, identified generally at“D2.” The front clearance D2 is defined between the back plate 620 ofthe right impeller 536 and an annular ridge 630 on the right pumphousing 550 where the volute surface 604 intersects the surface definingthe chamber 608. The clearance D2 is indicative of the degree to whichthe vanes 622 of the second impeller 536 extend into the chamber 608 andout of the volute chamber 606. The clearance D2 is also indicative ofthe size of an annular opening or aperture 632 defined between the backplate 620 and the ridge 630. The aperture 632 defines the area throughwhich the second impeller 536 pumps fluid through the volute chamber606. As D2 decreases, the area of the aperture 632 decreases as thevanes 622 of the second impeller 536 move or extend further out of thevolute chamber 606 into the chamber 608. Conversely, as D2 increases,the area of the aperture 632 increases as the vanes 622 of the secondimpeller 536 move or extend further out of the chamber 608 into thevolute chamber 606.

In the configuration shown in FIG. 12, left pump 542 performanceimproves as D1 decreases and right pump 552 performance improves as D2increases. During operation of the blood pump 500, the rotor assembly530 can move or shuttle axially relative to the stator assembly 520 dueto hydrodynamic pumping forces created by the left and right pumps 542and 552. The rotor assembly 530 can move axially between a leftposition, in which D1 and D2 are maximum, and a right position, in whichD1 and D2 are minimum.

When the rotor assembly 530 moves axially between the left and rightpositions, the configurations or geometries of the left and right pumps542 and 552 are altered. As the axial position of the left impeller 534changes, the clearance D1 between the left impeller and back surface 578of the left pump housing 540 changes, which alters the configuration andgeometry of the left pump 542 and left pump chamber 544. As the axialposition of the right impeller 536 changes, the clearance D2 between theright impeller and the right pump housing 550, which alters the size ofthe aperture 632, the configuration and geometry of the right pumpchamber 554, and the configuration or geometry of the right pump 552.

As the D1 clearance increases and the D2 clearance decreases, the firstand second pumps 542 and 552 decrease hydraulic output. Thus, for agiven pump speed, as the impellers 534 and 536 move toward the statorassembly 522 (i.e., reducing D1 and increasing D2), the pumps 542 and552 increase hydraulic output and pressure and flow increaseaccordingly. Conversely, as the impellers 534 and 536 move away from thestator assembly 522 (i.e., increasing D1 and decreasing D2), the pumps542 and 552 decrease hydraulic output and pressure and flow decreaseaccordingly.

It will thus be appreciated that, for the single motor, two-stageconfiguration of the blood pump 500 of the present invention, axialmovement of the rotor assembly 530 that produces increased pressure andflow at the left pump stage 542 will also produce a decrease in pressureand flow at the right pump stage 552. Similarly, axial movement of therotor assembly 530 that produces increased pressure and flow at theright pump stage 552 will also produce a decrease in pressure and flowat the left pump stage 542. From this, it follows that, for any givenspeed of the blood pump 500, the pressures and flows of the left andright pump stages 542 and 552 can be balanced if the axial position ofthe rotor assembly 530 relative to the stator assembly 520 is adjustedto the proper position.

Based on this principle, using the blood pump 500, systemic andpulmonary pressure and flow characteristics can be controlled throughadjusting the axial position of the rotor assembly 530. In theembodiment of FIGS. 9-12, the axial position of the of the rotorassembly 530 and, thus, the geometry or configuration of the left andright pumps 542 and 552 can is controlled passively.

In the passive control configuration of the blood pump 500, the axialposition of the rotor assembly 530 is controlled passively or inherentlythrough hydraulic forces created by the left and right pumps 542 and 552during operation.

In operation, the control algorithm executed by the controller adjustspump speed to provide a nominal systemic flow. Balanced systemic andpulmonary flows are achieved by adjusting of the axial position of therotor assembly 530. The axial adjustments of the rotor assembly 530occur inherently or automatically as a result of the configurations ofthe left and right impellers 534 and 536 and due to hydraulic pressures.Referring to FIG. 13, the control of speed of the pump 500 is based uponthe characteristic mathematical relationship between speed, electricpower consumption, and equilibrium output flow. In FIG. 13, net wattsare equal to the electric power supplied to the motor minus the bearingdrag power/motor efficiency and is calculated as the console power minusthe power required to run the motor without impellers, where SystemicVascular Resistance (SVR)=500-2000 dyne-sec/cm⁵ and Pulmonary VascularResistance (PVR)=100-500 dyne-sec/cm⁵. Also, in FIG. 13, KRPM is motorrpm/1000. The current response to speed pulses will also allowestimation of systemic vascular resistance, which can be correlated tothe change in power consumption with speed.

Because the axial hydrodynamic forces acting on the back plate portions610 and 620 of the impellers 534 and 536 are primarily those created bypump inlet pressures, the axial position of the rotor assembly 530adjusts in response to pressure differentials between the left and rightinlet portions 592 and 602. As the axial position of the rotor assembly530 adjusts, the geometry and hydraulic performance of the left andright pumps 542 and 552 changes, as described above. This produces acorresponding change or adjustment in the outlet flows and pressures ofthe left and right pumps 542 and 552, trading pressure and flowperformance between the two pumps. The blood pump 500 is thus configuredwith a self-adjusting rotor assembly 530 that helps balance pulmonaryand systemic flows, as well as atrial pressures, through incrementalchanges the hydraulic performance of the left and right pumps 542 and552.

When operating in high clearance, minimum pump performance occurs whenthe pumping vanes are centered in the axial clearance (front and backclearances equal). Therefore, performance can be modulated by moving theimpellers 534 and 536 in either axial direction. Maximum performance forthe left pump 542 occurs when back clearance D1 is minimum, whilemaximum performance for the right pump 552 occurs when front clearanceD2 is maximum. The passive control implemented in the embodiment ofFIGS. 9-12 modulates performance by adjusting the clearances D1 and D2.The advantage of using the back (inside) edges to modulate performanceis that hydraulic forces operating on the rotating assembly can enforcethe correct direction of axial movement for passive control, therebyeliminating the need for an active axial control system.

In the embodiment of FIGS. 9-12, the left pump 542 is configured to havea steep pressure rise vs. flow characteristic and also to regulateperformance via the impeller vane clearance D1 such that the left pumpoutput increases as the rotating assembly moves to the right as viewedin FIG. 12. The right pump 552 is configured to regulate performance bycreating an aperture 632 that controls impeller vane discharge,decreasing output as the rotating assembly moves to the right (in FIG.12), and increasing output as the rotating assembly moves to the left.

Advantageously, the configuration is self-regulating. In response to achanging vascular resistance, the rotating rotor assembly 530 moves inthe direction of lowest inlet pressure to automatically correctimbalances between the inlet pressures at the left and right inlets 546and 556. Thus, for example, in the case of inlet obstruction due to leftatrial suction, the left inlet pressure drops and the rotating assemblymoves to the left, i.e., in the direction of low pressure. This resultsin decreased left pump performance simultaneous with increased rightpump performance, which automatically corrects the suction condition.The pump 500 would operate similarly and correspondingly to selfregulate in the event of right atrial suction.

A blood pump 700 according to a fifth embodiment of the presentinvention is illustrated in FIGS. 14-16. The blood pump 700 of FIGS.14-16 has a configuration that is similar to the embodiments of FIGS.9-12 and has a two-stage or dual centrifugal pump configuration. Theblood pump 700 may thus be configured for use as a total artificialheart (TAH) device. The blood pump 700 could, however, be suitable fornon-TAH implementations, such as biventricular support or anyimplementation in which a dual or two stage fluid handling pump withpressure balancing features is desired.

FIGS. 14-16 illustrate the blood pump 700 in different positions thatare described in detail below. Referring to FIG. 14, the blood pump 700includes a stator assembly 720, a rotor assembly 730, a left pumphousing 740, and a right pump housing 750. In an assembled condition ofthe blood pump 700, the rotor assembly 730 is supported by the statorassembly 720 for rotation about an axis 712. The pump housings 740 and750 are fixed to the stator assembly 720 to enclose the rotor assembly730. The rotor assembly 730 includes a motor rotor 732, a first or leftimpeller 734, and a second or right impeller 736.

The motor rotor 732 includes a core 760 surrounded or otherwise encasedin a shell or casing 764 upon which a ring-shaped permanent magnet 762is mounted. The core 760 may be constructed of a low densitymagnetically permeable material and may include hollow cavities 766 thathelp make the rotor assembly 730 a neutral buoyancy rotating assemblythat is insensitive to the attitude of the pump 700. The core 760supports a magnet core 761 constructed, for example, of steel, that inturn supports the magnet 762 for rotation with the motor rotor 732. Theleft and right impellers 734 and 736 may be secured to the core 760 byknown means, such as adhesives, mechanical fasteners, or, could beformed as a single piece of material with the shell 764 via molding. Inthe embodiment illustrated in FIGS. 14-16, the impellers 734 and 736 aresecured to the core 760 via threaded connections 768.

The stator assembly 720 includes a stator housing 722 that supports amotor stator 724. The motor stator 724 includes a stator core and motorwindings, illustrated schematically at 726 and 728, respectively in FIG.14. The motor windings 728 are electrically connected to a control cable(not shown). The rotor magnet 762 is shorter than the motor windings 728to allow a controlled amount of free axial movement of the rotorassembly 730.

The blood pump 700, when assembled, includes a centrifugal first or leftpumping stage or pump 742. The left pump 742 includes the left impeller734 and a left pump chamber 744 in which the left impeller is disposed.The left pump chamber 744 is defined, at least partially, by the leftpump housing 740 and the stator assembly 720. The left pump 742 alsoincludes a left pump inlet 746 and a left pump outlet 748 that, in theillustrated embodiment, are formed as integral portions of the left pumphousing 740. The left pump housing 740 includes an inlet surface 790that helps define an inlet portion 792 of the left pump chamber 744 influid communication with the inlet 746. The left pump housing 740 alsoincludes a volute surface 794 that helps define a volute portion 796 ofthe left pump chamber 744 in fluid communication with the outlet 748.

The blood pump 700, when assembled, also includes a centrifugal secondor right pumping stage or pump 752. The right pump 752 includes theright impeller 736 and a right pump chamber 754 in which the rightimpeller is disposed. The right pump chamber 754 is defined, at leastpartially, by the right pump housing 750 and the stator assembly 720.The right pump 752 also includes a right pump inlet 756 and a right pumpoutlet 758 that, in the illustrated embodiment, are formed as integralportions of the right pump housing 750. The right pump housing 750includes an inlet surface 800 that helps define an inlet portion 802 ofthe right pump chamber 754 in fluid communication with the inlet 756.The right pump housing 750 also includes a volute surface 804 that helpsdefine a volute portion 806 of the right pump chamber 754 in fluidcommunication with the outlet 758. The right pump housing 750 furtherincludes a chamber 808 adjacent the volute portion 806.

The motor rotor 732 and motor stator 724 help define a motor 780 of theblood pump 700 that drives the left and right pumps 742 and 752. Themotor 780 may be any type of electric motor suited to drive the pumps742 and 752 and deliver the desired performance characteristics. Forexample, in the illustrated embodiment, the motor 780 may have a singlephase or multi-phase brushless, sensorless DC motor configuration. Amotor controller (not shown) is operative to excite the phase windings728 of the motor 780 to achieve desired performance of the motorportion, such as motor speed or current. For example, the motorcontroller may apply pulse width modulated voltage to the motor phasesin order to achieve the desired motor/pump performance.

The first impeller 734 includes a back plate 810 and a plurality ofvanes 812 that extend radially from the rotor 730. The vanes 812 mayinclude first or primary vanes and second or splitter vanes. The vanes812 may be configured with a low incidence inlet and a radial discharge.The second impeller 736 includes a back plate 820 and a plurality ofvanes 822 that extend radially along the end face of the rotor 730. Thevanes 822 may, for example, include first or primary vanes and second orsplitter vanes that may be configured with a low incidence inlet and aradial discharge. Those skilled in the art will appreciate that theimpellers 734 and 736 could have alternative configurations.

The back plates 810 and 820 are aligned axially with the inlet portions792 and 802 of the left and right pump chambers 744 and 754,respectively. Therefore, fluid pressures acting on the back plates 810and 820 are primarily inlet pressures and thus exert forces on the rotorassembly 730 that are primarily axial, i.e., parallel to the axis 712.Outlet pressures produced by the blood pump 700 are generated primarilyat the end portions of the vanes 812 and 822.

During operation of the blood pump 700, the rotor assembly 730 rotatesabout the axis 712 relative to the stator assembly 720. The rotorassembly 730 is supported or rides on a hydrodynamic or fluid filmbearing formed by the pumped fluid, i.e., blood. Alternatively, theblood pump 700 could include other types of bearing features, such asmechanical bearings or bearing surfaces formed from or coated with lowfriction materials, for facilitating rotation of the rotor assembly 730.As a further alternative, the rotor assembly 730 could be magneticallysuspended.

The materials used to construct the blood pump 700 may be formed frommaterials conducive to blood pumping implementations. For example,portions of the blood pump 700 that are exposed to blood flow duringuse, such as the impellers 734 and 736 and pump housings 740 and 750,may be formed from, coated, or encased in a biocompatible material, suchas stainless steel, titanium, ceramics, polymeric materials, compositematerials, or a combination of these materials. Surfaces or portions ofthe blood pump 700 that may contact each other during use, such as theleft impeller 734 and pump housing 740, the right impeller 736 and pumphousing 750, or the rotor casing 764, may also be formed or coated withlow friction materials, such as a fluorocarbon polymer coatings,diamond-like carbon coatings, ceramics, titanium, and diamond coatedtitanium.

According to the present invention, the blood pump 700 is configuredwith a clearance that permits axial movement (left/right movement asshown in FIGS. 14-16) of the rotor assembly 730 relative to the statorassembly 720 during operation of the pump. In FIG. 14, the rotorassembly 730 is in a center position about midpoint in this axialclearance. FIG. 15 illustrates the rotor assembly 730 in a full-leftposition of this axial clearance. FIG. 16 illustrates the rotor assembly730 in a full-right position of this axial clearance.

The axial clearance of the blood pump 700 creates an axial backclearance between the left impeller 734 and the left pump housing 740identified generally at “E1.” As shown in FIG. 14, E1 is the clearancebetween the vanes 812 of the left impeller 734 and a back surface 778 ofthe left pump chamber 744, which may be defined at least partially bythe stator assembly 720, the left pump housing 740, or both the statorassembly and the left pump housing. During operation of the pump 700,when the rotor assembly 730 moves axially relative to the statorassembly 720, the left impeller 734 moves axially within the left pumpchamber 744. In the embodiment illustrated in FIGS. 14-16, the leftimpeller 734 is positioned within the volute portion 796 of the leftpump chamber 744 throughout the range of axial movement of the rotorassembly 730.

The axial clearance of the blood pump 700 creates an axial frontclearance between the right impeller 736 and the right pump housing 750,identified generally at “E2.” The front clearance E2 is defined betweenthe back plate 820 of the right impeller 736 and an annular ridge 830 onthe right pump housing 750 where the volute surface 804 intersects thesurface defining the chamber 808. The clearance E2 is indicative of thedegree to which the vanes 822 of the second impeller 736 extend into thechamber 808 and out of the volute chamber 806. The clearance E2 is alsoindicative of the size of an annular opening or aperture 832 definedbetween the back plate 820 and the ridge 830. The aperture 832 definesthe area through which the second impeller 736 pumps fluid through thevolute chamber 806. As E2 decreases, the area of the aperture 832decreases as the vanes 822 of the second impeller 736 move or extendfurther out of the volute chamber 806 into the chamber 808. Conversely,as E2 increases, the area of the aperture 832 increases as the vanes 822of the second impeller 736 move or extend further out of the chamber 808into the volute chamber 806.

During operation of the pump 700, the rotor assembly 730 can move orshuttle freely in axial directions relative to the stator assembly 720due to hydrodynamic pumping forces created by the left and right pumps.The motor windings 728, being longer than the rotor magnet 762, do notexert an axial pull on the rotor 732, and therefore do not resistaxially shuttling of the rotor, as long as the rotor magnet ispositioned within the length of the windings. If the rotor 732 attemptsto travel axially beyond the length of the windings 728, it ismagnetically constrained in order to prevent contact between the rotorand the pump housings 740 and 750. Additionally, the rotor assembly 730,being neutrally buoyant in blood, helps make the pump 700 insensitive topositional or attitudinal changes during use.

When shuttling due to hydrodynamic pumping forces, the rotor assembly730 can move axially between the full-left position (FIG. 15), in whichE1 and E2 are maximum, and the full-right position (FIG. 16), in whichE1 and E2 are minimum. When the rotor assembly 730 moves axially betweenthe left and right positions, the configurations or geometries of theleft and right pumps 742 and 752 can change. The degree to which theconfigurations or geometries of the left and right pumps 742 and 752change in response to this axial shuttling depends on the configurationof the pumping chambers 744 and 754, the configuration of the impellers734 and 736, and the relative spatial relationships of these parts whenthe rotor assembly 730 moves axially.

Adjusting the geometries or configurations of the left and right pumps742 and 752 results in a corresponding adjustment of the hydraulicperformance characteristics of the pumps. By “hydraulic performance” itis meant to refer to a term of art that is well-known to those havingskill in the art of fluid dynamics and pump design. The hydraulicperformance of a centrifugal pump is defined by the relationship, forthat particular pump, between volumetric flow, differential pressure(inlet-outlet pressure rise), and pump speed. That is, measuring pumphydraulic performance is based on the principle that for any given pumparchitecture, at a given pump speed and system pressure, the pump willproduce a specific volumetric flow rate. This allows hydraulicperformance to be a standard, fundamental benchmark used to quantify andcompare centrifugal pumps.

Those skilled in the art will appreciate that, in a TAH scenario, it iscritical to balance pulmonary and systemic arterial blood flows andatrial pressures. For example, if the right pump 752 delivers blood at ahigher flow rate than the left pump 742, blood may accumulate in thelungs. As another example, if the left pump 742 delivers blood at ahigher flow rate than the right pump 752, blood may accumulate in theliver and other internal organs, leading to organ failure. The goal forthe blood pump 700 is thus to balance pulmonary and systemic arterialblood flows and atrial pressures. According to the present invention,the blood pump 700 balances systemic and pulmonary atrial pressures andarterial flow rates by adjusting the geometry or configuration of theleft (systemic) pump 742 and right (pulmonary) pump 752.

Based on the above, the blood pump 700 is configured to control systemicand pulmonary pressure and flow characteristics through adjusting theaxial position of the rotor assembly 730 in order to adjust thehydraulic performance characteristics of the left and right pumps 742and 752. In the embodiment of FIGS. 14-16, the axial position of the ofthe rotor assembly 730 and, thus, the geometry or configuration of theleft and right pumps 742 and 752 is controlled passively. In thispassive control configuration of the blood pump 700, the axial positionof the rotor assembly 730 is controlled inherently or automatically bythe hydraulic forces created by the left and right pumps 742 and 752during operation.

Those skilled in the art will appreciate the fact that, in the humanbody, normal systemic blood pressure is more than three times normalpulmonary blood pressure. Thus, in a total artificial heart (TAH)environment, the left (systemic) pump 742 performs more than three timesthe amount of work than that performed by the right (pulmonary) pump752. Therefore, one skilled in the art will appreciate that it may bedesirable, for the sake of conserving power and efficiency, to adjustthe hydraulic performance of the right pump 752 while maintainingrelatively consistent left pump 742 performance since the right pump 752performs substantially less work than the left pump 742. According tothe present invention, the pump 700 of FIGS. 14-16 achieves, at leastsubstantially, this purpose.

In operation, the control algorithm executed by the controller adjustspump speed to provide a nominal systemic flow. Balanced systemic andpulmonary flows are achieved by adjusting the axial position of therotor assembly 730. Axial movement of the rotor assembly 730 to theright as viewed in FIGS. 14-16 decreases pressure and flow at the rightpump 752. Axial movement of the rotor assembly 730 to the left as viewedin FIGS. 14-16 produces increased pressure and flow at the right pump752. From this, it follows that, for any given speed of the pump 700,the pressures and flows of the left and right pumps 742 and 752 can bebalanced if the axial position of the rotor assembly 730 relative to thestator assembly 720 is adjusted to the proper position. Based on thisprinciple, the pump 700 can control relative systemic and pulmonarypressure and flow characteristics through adjusting the axial positionof the rotor assembly 730.

Because the axial hydrodynamic forces acting on the back plate portions810 and 820 of the impellers 734 and 736 are primarily those created bypump inlet pressures, the axial position of the rotor assembly 730adjusts in response to pressure differentials between the left and rightinlet portions 792 and 802. As the axial position of the rotor assembly730 adjusts, the geometry and hydraulic performance of the right pump752 changes, as described above. This produces a corresponding change oradjustment in the outlet flows and pressures of the right pump 752 untilthe pressures at the inlets 792 and 802 are balanced. The blood pump 700is thus configured with a self-adjusting rotor assembly 730 that helpsbalance pulmonary and systemic flows, as well as atrial pressures,through incremental changes in the hydraulic performance of the rightpump 752.

Advantageously, the configuration is self-regulating. In response to achanging vascular resistance, the rotating rotor assembly 730 moves inthe direction of lowest inlet pressure to automatically adjust thegeometries of the left and right pumps 742 and 752, which adjusts therelative hydraulic performance characteristics of the pumps and therebycorrects imbalances between the inlet pressures at the left and rightinlets 746 and 756. Because unbalanced atrial pressures are the resultof imbalanced flows, drawing the pressures to balance also results inbalanced flows. Thus, for example, in the case of inlet obstruction dueto left atrial suction, the left inlet pressure drops and the rotatingassembly moves to the left, i.e., in the direction of low pressure. Thisresults in increased right pump performance, which fills the left atriumand thereby automatically corrects the suction condition. In the case ofright suction, the rotating assembly would move to the right, closingthe aperture 832, thereby reducing the right pump 752 performance andautomatically correcting the right suction condition.

Those skilled in the art will appreciate that the degree or manner inwhich the configurations or geometries of the left and right pumps 742and 752 change in response to axial shuttling of the rotor assembly 730depends on the individual configurations of the respective pumpinghousings 740 and 750 and impellers 734 and 736 and on the spatialrelationships of these structures. Therefore, the degree or manner inwhich the hydraulic performance characteristics of the left and rightpumps 742 and 752 change in response to axial shuttling of the rotorassembly 730 also depend on these characteristics. Further, the degreeto which the configuration, geometry, and hydraulic performance of theleft and right pumps 742 and 752 are adjusted can be tailoredindividually to the pumps. For example, in the embodiment of the presentinvention illustrated in FIGS. 14-16, the housing 740 and impeller 734of the left pump 742 are configured to minimally adjust the hydraulicperformance characteristics of the left pump in response to axialshuttling of the rotor assembly 730. Conversely, the housing 750 andimpeller 736 of the right pump 752 are configured to substantiallyadjust the hydraulic performance characteristics of the right pump inresponse to axial shuttling of the rotor assembly 730.

Regarding the left pump 742, according to the present invention, theleft impeller 734 is positioned within the volute portion 796 throughoutthe entire range of motion. As the rotor assembly 730 shuttles axiallyfrom the full-left position of FIG. 15 to the full-right position ofFIG. 16, a clearance is maintained between the left impeller 734 and theleft housing. As a result, the geometry and the hydraulic performance ofthe left pump 742 remains relatively constant as the rotor assembly 730shuttles between these two extremes.

Regarding the right pump 752, as the rotor assembly 730 shuttlesaxially, the right impeller 736 moves between the volute portion chamber806 and chamber 808. Blood entering the right pump 752 must pass throughchamber 808 into the volute portion 806 via the aperture 832. The sizeof the aperture 832, defined by the clearance E2, adjusts depending onthe axial position of the impeller. As this clearance E2 increases, theportion of the right impeller 736 positioned in the volute portion 806versus the portion positioned in the chamber 808 increases and thehydraulic output of the right pump 752 increases. As this clearance E2decreases, the portion of the right impeller 736 positioned in thevolute portion 806 versus the portion positioned in the chamber 808decreases and the hydraulic output of the right pump 752 decreases.Thus, as the rotor assembly 730 shuttles between the full-left positionof FIG. 15 to the full-right position of FIG. 16, the right impeller 736goes from being positioned fully within the volute portion 806 to fullywithin the chamber 808. Since the portion of the right impeller 736positioned in the chamber 808 is substantially inhibited fromcontributing to the pumping action of the right pump 752, the change inthe configuration or geometry of the right pump varies substantially asthe rotor assembly 730 shuttles axially . It is due to this that thehydraulic performance of the right pump 752 varies substantially as therotor assembly 730 shuttles between these two extremes.

When the inlet (atrial) pressure at the left pump 742 is higher than theinlet (atrial) pressure at the right pump 752 (for example, due to rightover pumping or left under pumping), the rotor assembly 730 is shiftedby hydraulic forces to the right, thereby closing the right pumpaperture 832 and decreasing the right pump hydraulic performance.Conversely, when the inlet (atrial) pressure at the left pump 742 islower than the inlet (atrial) pressure at the right pump 752 (forexample, due to right under pumping or left over pumping), the rotorassembly 730 is shifted by hydraulic forces to the left, thereby openingthe right pump aperture 832 and increasing the right pump hydraulicperformance. From this, it follows that, for any given speed of theblood pump 700, the pressures and flows of the left and right pumpstages 742 and 752 can be balanced if the axial position of the rotorassembly 730 relative to the stator assembly 720 adjusts to the properposition.

To illustrate how the left and right pumps 742 and 752 respond tovarying inlet (atrial) pressure differentials, the hydraulic performanceof the left and right pumps 742 and 752 is illustrated in FIG. 17. FIG.17 illustrates a chart or diagram that plots pressure vs. flow curvesfor the left and right pumps 742 and 752 for a given pump speed of 2700rpm pumping a solution of Water and Glycerin at a specific gravity ofabout 1.06 to mimic pumping blood. FIG. 17 illustrates the hydraulicperformance of the left and right pumps 742 and 752 equal flow of thepumps with inlet (atrial) pressure differentials that range from −10 to+10 mmHg. As shown in FIG. 17, the hydraulic performance of the leftpump 742 varies very little between these extremes. The hydraulicperformance of the right pump, however, varies greatly and thereforeaccounts for a majority of the hydraulic performance regulation of thepump 700.

Referring to FIG. 17, by way of example illustration, consider ascenario in which the inlet pressure at the left pump 742 is 6 mmHghigher than the inlet pressure at the right pump 752. This could be theresult, for example, of a physiological change that creates a variationin fluid flow resistance in one or both of the systemic and pulmonarysystems. In this situation, the left and right pumps 742 and 752 areoperating on hydraulic performance curves that lie between therespective extremes in FIG. 17. Since axial shifting produces relativelylittle change in the hydraulic performance of the left pump 742, themajority of the pressure compensation is seen at the right pump 752.Since the right pump 752 in this scenario begins with an inlet pressuredeficiency (−6 mmHg), the curve (not shown) upon which the right pump isoperating would shift downward as viewed in FIG. 17. As a result, thehydraulic performance of the right pump would decrease, causing aresultant increase in inlet pressure at the right pump, moving the inletpressure differential toward zero, thereby correcting the atrialpressure imbalance.

Comparing the chart of FIG. 17 to the charts of FIGS. 18 and 19illustrates how the different pump geometries result in differenthydraulic performance characteristics of the pumps. FIG. 18 illustratesthe hydraulic performance characteristics of the pump 500 of FIG. 12. InFIG. 18, a chart or diagram plots pressure vs. flow curves for the leftand right pumps 542 and 552 for a given pump speed of 2100 rpm pumping asolution of Water and Glycerin at a specific gravity of about 1.06 tomimic pumping blood. FIG. 18 illustrates the hydraulic performance ofthe left and right pumps 542 and 552 equal flow of the pumps with inlet(atrial) pressure differentials that range from −10 to +10 mmHg.

FIG. 18 illustrates that the hydraulic performance of the left pump 542and right pump 552 both vary between these extremes and thus bothcontribute to the hydraulic performance regulation of the pump 500. Asillustrated in FIG. 18, there is a threshold effect for the left pump542 (at 3.5 LPM, 2100 rpm), but it is only at low flows. So, in the caseof extreme operating conditions, the left pump performance will increaseas needed to keep a minimum flow for a given speed.

FIG. 19 illustrates the hydraulic performance characteristics of thepump 10 of FIG. 2. In FIG. 19, a chart or diagram plots pressure vs.flow curves for the left and right pumps 42 and 52 for a given pumpspeed of 1500 rpm pumping a solution of Water and Glycerin at a specificgravity of about 1.06 to mimic pumping blood. FIG. 19 illustrates thehydraulic performance of the left and right pumps 42 and 52 for extremeleft and right axial positions of the rotating assembly.

FIG. 19 illustrates that the hydraulic performance of both the left pump42 provides essentially all of the performance variation and regulationof the pump 10. As Al becomes small, the performance transforms at acertain flow rate, proportional to speed. FIG. 19 illustrates that, forthe configuration of the pump 10 of FIG. 2, the left pump 42 transitionsfrom exhibiting centrifugal pump characteristics to regenerative pumpcharacteristics at a certain value of flow coefficient [flow/speed]. Ifthe left atrial pressure is high due to low relative left performance,the rotating assembly moves to the right, Al becomes smaller, and theperformance of the left pump increases. Because of the threshold effectshown in FIG. 19, it will automatically tend to hold the threshold flow(6 LPM at 1500 rpm). Therefore, flow tends to be both balanced andproportional to speed.

Those skilled in the art will appreciate that it may be desirable fornominal operation of the pump 700 to be biased to run with the leftatrial pressure slightly higher, e.g., 3 mmHg higher, than right inletpressure so as to be consistent with normal hemodynamic values of thehuman body. According to the present invention, this is achieved byadjusting the cross-sectional area of the left pump inlet 746 to besmaller than the cross-sectional area of the right pump inlet 756 inorder to create a pressure drop at the left pump 742. As shown in FIGS.14-16, the left pump inlet 746 has a diameter E3 that is smaller thanthe diameter E4 of the right pump inlet 756. As a result of the pressuredrop created by the reduced inlet diameter at the left pump 742, atrialpressures exerted on or “seen” at the left impeller 734 pump are lower(e.g., 3 mmHg lower) than actual at nominal target flow rates (5-6 Ipm).This causes the rotor assembly 730 to overcompensate by over-shifting tothe left and under-shifting to the right, as viewed in FIGS. 14-16.Thus, when the pump reaches equilibrium where the pump inletdifferential pressure is 0 mmHg, the atrial pressure differential willactually be approximately +3 mmHg in favor of the left. The addedpressure drop at the left inlet also aids with opening the right pumpaperture 832 more fully at high flows.

A sixth embodiment of the present invention is illustrated in FIG. 20.The embodiment of FIG. 20 illustrates a motor 850 that can beimplemented in any of the pump designs herein. The motor 850 includes astator 860 and a rotor 880 that are aligned coaxially along a motor axis852. The rotor 880 is encircled by the stator 860 and rotatable relativeto the stator about the axis 852.

In the embodiment illustrated in FIG. 20, the stator 860 includes twolaminations 862 separated by a non-magnetic spacer 864. The laminationsmay be constructed, for example, of steel. The laminations 862 andspacer 864 are stacked to form a core 868 of the stator 860. Thelaminations 862 thus form axial end portions of the core 868. The motorwindings 866 are wound around the lamination-spacer stack, i.e., thecore 868.

The rotor 880 has a hollow cylindrical core 882 upon which two magnetassemblies 884 are mounted. The magnet assemblies 884 encircle the core882 and extend along axial end portions of the core. The core 882 may beconstructed of a ferrous material, such as steel. The magnet assembliesare separated by a non-magnetic spacer 886. The spacer 886 encircles thecore 882 and extends along a central portion of the core between themagnet assemblies 884. The magnet assemblies 884 correspond withrespective ones of the laminations 862. The spacers 886 and 864correspond with each other.

According to the embodiment of FIG. 20, the separate, spaced pairs oflaminations 862 and magnet assemblies 884 act as separate drivers forthe motor 850 and the spacers 886 and 864 provide a gap in the magneticproperties of the magnet assemblies and laminations. Each magnetassembly 884 has an axial length that is shorter than its correspondinglamination 862. This allows the rotor 880 to move or shuttle axiallyrelative to the stator 860 within the axial length of the laminations862 during motor operation. The length or distance along which the rotor880 can shuttle axially relative to the stator 860, generally speaking,is equal to the axial length of the laminations 862 minus the axiallength of the magnet assemblies 884. In FIG. 20, the free axial isindicated generally by the arrows labeled “D.”

Advantageously, the embodiment of FIG. 20 improves the axial stiffnessof the motor 850. If/when the rotor 880 is urged to move axially toposition the magnets 884 beyond the axial extent of the laminations 862,there are now two magnetic forces that resist this movement, namelythose of the left and right magnet/lamination pairs. If the rotortravels axially beyond the laminations, these dual-acting pairs urge therotor 880 back into position with a greater total amount of magneticforce. Accordingly, the motor 850 of FIG. 20 provides a window of freeaxial motion limited by a strong magnetic restoring force as the rotor880 motor moves beyond bounds at the ends of free motion. This allowsthe self-regulating action of the various pumps described herein whilepreventing the rubbing of the rotating assembly (motor rotor andimpellers) against the blood pump housing. For example, this window offree axial movement may be about 0.04 inches in each direction.

As another advantage, the embodiment of FIG. 20 improves the axialstiffness without increasing the radial load on the magnetic bearing.Since the two magnet 884/two lamination 862 designs place spacers 864,886 (e.g., plastic) between the laminations 862 and magnets 884,respectively, the overall weight of the rotor 880 can be reduced,thereby helping to achieve the goal of neutral buoyancy of the rotatingassembly.

Additionally, according to the embodiment of FIG. 20, another feature ofthe motor 850 is the ability to track the axial position of the rotor880 in real time and transmit the rotor position to the motor controllerwithout the addition of any extra conductors between the motor and themotor controller. For any implantable motor it is desirable to have asfew conductors (wires) between the motor and the motor controller aspossible in order to thereby reduce cable complexity and size. The motor850 is a sensorless, brushless DC (SLBLDC) motor that requires onlythree conductors for full control of speed and torque.

The rotor position monitoring system (RPMS) of the embodiment of FIG. 20uses Hall sensor(s) to detect the axial position of the rotor 880 andtransmits the position data over two of the already existing motorconductors 900 without interfering with the normal control of the motor850. The power required to run the rotor position circuit is alsoscavenged from the existing three motor wires. The RPMS consists of apower scavenging circuit, a Hall sensor(s) 904 and a voltage tofrequency convertor circuit 906 which modulates a carrier frequency thatis in a band above the frequency band used to control the motor. Therotor axial position is then recovered in the motor controller 908 byisolating the rotor position band with an active filter and demodulatingthe rotor position signal with a frequency to voltage convertor.Advantageously, since the axial position of the rotor 880 is directlyrelated to the differential pressure between the left and right sides ofthe pump, the rotor axial position monitoring feature provides importanthemodynamic information.

From the above description of the invention, those skilled in the artwill perceive improvements, changes and modifications. For example, inthe embodiment of FIG. 20, further adjustments/improvements to the axialstiffness of the motor 850 could be realized through additionalmagnet/lamination pairs (e.g., three or more). Such improvements,changes and modifications within the skill of the art are intended to becovered by the appended claims.

Having described the invention, the following is claimed:
 1. A pumpcomprising: a housing; at least one impeller; and a motor for impartingrotation to the at least one impeller, the motor comprising: a statorsupported in the housing; and a rotor assembly comprising a rotorsupported in the housing for rotation relative to the stator about anaxis; the stator comprising a stator core comprising first and secondlaminations spaced from each other along the length of the stator core,and motor windings wound around the first and second laminations; therotor comprising a rotor core; a first magnet assembly that extendsaround an axial portion of the rotor core and a second magnet assemblythat extends around a second axial portion of the rotor core, the firstand second magnet assemblies being spaced from each other along thelength of the rotor, wherein the first lamination and first magnetassembly act as a first driver for the motor, and the second laminationand second magnet assembly act as a second driver for the motor, thepump further comprising: a first impeller operatively coupled to a firstaxial end of the rotor for rotation with the rotor about the axis; and asecond impeller operatively coupled to a second axial end of the rotor,opposite the first axial end, for rotation with the rotor about theaxis, the rotor assembly being movable along the axis relative to thehousing to adjust hydraulic performance characteristics of the pump;wherein the pump is configured such that fluid inlet pressures acting onthe first impeller exerts an axial force on the rotor assembly in afirst direction along the axis and fluid inlet pressures acting on thesecond impeller exerts an axial force on the rotor assembly in a seconddirection along the axis, opposite the first direction.
 2. The pumprecited in claim 1, wherein the first lamination has an axial lengththat is greater than an axial length of the first magnet assembly, andthe second lamination has an axial length that is greater than an axiallength of the second magnet assembly, which during operation of themotor permits free axial movement of the rotor assembly relative to thestator while the magnet assemblies are positioned axially within thelength of their corresponding laminations.
 3. The pump recited in claim1, wherein the first lamination has an axial length that is greater thanan axial length of the first magnet assembly, and the second laminationhas an axial length that is greater than an axial length of the secondmagnet assembly, which during operation of the motor constrains therotor assembly from moving relative to position the magnet assembliesaxially beyond the length of their corresponding laminations.
 4. Thepump recited in claim 1, further comprising a first spacer thatencircles the stator core and extends axially along a portion of thestator core between the first and second laminations.
 5. The pumprecited in claim 1, further comprising a second spacer that encirclesthe rotor core and extends axially along a portion of the rotor corebetween the first and second magnet assemblies.
 6. The pump recited inclaim 1, further comprising: a Hall sensor for detecting the axialposition of the rotor relative to the stator and generates a positionsignal indicative of this position; a voltage to frequency convertorcircuit that modulates a carrier frequency that is in a band differentthan the frequency band used to control the motor, the position signalbeing carried to a motor controller at the carrier frequency over wiresthat are used to power the motor.
 7. The pump recited in claim 1,wherein the rotor is of neutral buoyancy in blood.
 8. The pump recitedin claim 1, wherein the rotor comprises a magnet and the statorcomprises motor windings, the magnet having an axial length that isshorter than an axial length of the motor windings.
 9. A pumpcomprising: a housing; at least one impeller; and a motor for impartingrotation to the at least one impeller, the motor comprising: a statorsupported in the housing; a rotor assembly comprising a rotor supportedin the housing for rotation relative to the stator about an axis;wherein the stator comprises a stator core comprising first and secondlaminations spaced from each other along the length of the stator core,and motor windings wound around the first and second laminations; andwherein the rotor comprises a rotor core; a first magnet assembly thatextends around an axial portion of the rotor core and a second magnetassembly that extends around a second axial portion of the rotor core,the first and second magnet assemblies being spaced from each otheralong the length of the rotor, wherein the first lamination and firstmagnet assembly act as a first driver for the motor, and the secondlamination and second magnet assembly act as a second driver for themotor, the pump also comprising: a first impeller operatively coupled toa first axial end of the rotor for rotation with the rotor about theaxis; and a second impeller operatively coupled to a second axial end ofthe rotor, opposite the first axial end, for rotation with the rotorabout the axis; wherein the rotor assembly is movable along the axisrelative to the housing to adjust hydraulic performance characteristicsof the pump, the pump further comprising: a first pumping stagecomprising a first pump housing part that helps define a first pumpingchamber in which the first impeller is supported for rotation about theaxis, the first impeller being movable along the axis relative to thefirst pump housing part; and a second pumping stage comprising a secondpump housing part that helps define a second pumping chamber in whichthe second impeller is supported for rotation about the axis, the secondimpeller being movable along the axis relative to the second pumphousing part; the first and second impellers when moved along the axiswith the rotor assembly moving axially relative to the first and secondpump housing parts to adjust the hydraulic performance characteristicsof the first and second pumping stages.
 10. The pump recited in claim 9,wherein the first pump housing part and the first impeller areconfigured to respond to axial movement of the rotor assembly byadjusting the hydraulic performance characteristics of the first pumpingstage; and the second pump housing part and the second impeller areconfigured to respond to axial movement of the rotor assembly byadjusting the hydraulic performance characteristics of the secondpumping stage.
 11. The pump recited in claim 9, wherein the geometriesof the first impeller and the first pump housing part and the geometriesof the second impeller and the second pump housing part are configuredsuch that the hydraulic performance characteristics of the first pumpingstage adjust in response to axial movement of the rotor assembly with amagnitude different than the magnitude with which the hydraulicperformance characteristics of the second pumping stage adjust inresponse to the same axial movement of the rotor assembly.
 12. The pumprecited in claim 9, wherein at least one of the first and second pumpingstages comprises a pumping chamber and an adjacent chamber in fluidcommunication with the pumping chamber, the impeller associated with theat least one pumping stage having at least a portion movable into andout of the adjacent chamber from the pumping chamber in response toaxial movement of the rotor assembly.
 13. The pump recited in claim 12,wherein the adjacent chamber is positioned between the pumping chamberand an inlet of the at least one pumping stage, the at least one pumpingstage comprising an aperture defined between the impeller associatedwith the at least one pumping stage and a portion of a sidewall of apump housing part associated with the at least one pumping stage at ornear the interface between the pumping chamber and the adjacent chamber,the aperture having a size that varies depending on the axial positionof the impeller associated with the at least one pumping stage.
 14. Thepump recited in claim 12, wherein the portion of the associated impellerpositioned in the adjacent chamber is at least substantially inhibitedfrom pumping fluid through the associated pumping stage.
 15. The pumprecited in claim 1, wherein the axial forces exerted on the rotorassembly by the fluid inlet pressures acting on the first and secondimpellers adjusts the axial position of the rotor assembly to helpbalance the fluid inlet pressures acting on the first and secondimpellers.
 16. The pump recited in claim 1, further comprising a firstinlet associated with the first impeller, and a second inlet associatedwith the second impeller, the first and second inlets having differentinternal diameters.
 17. The pump recited in claim 16, wherein theinternal diameters of the first and second inlets are selected to be ofdifferent sizes that create differential inlet pressure drops to biasthe axial forces acting on the first and second impellers.
 18. The pumprecited in claim 9, wherein the first lamination has an axial lengththat is greater than an axial length of the first magnet assembly, andthe second lamination has an axial length that is greater than an axiallength of the second magnet assembly, which during operation of themotor permits free axial movement of the rotor assembly relative to thestator while the magnet assemblies are positioned axially within thelength of their corresponding laminations.
 19. The pump recited in claim9, wherein the first lamination has an axial length that is greater thanan axial length of the first magnet assembly, and the second laminationhas an axial length that is greater than an axial length of the secondmagnet assembly, which during operation of the motor constrains therotor assembly from moving relative to position the magnet assembliesaxially beyond the length of their corresponding laminations.
 20. Thepump recited in claim 9, further comprising a first spacer thatencircles the stator core and extends axially along a portion of thestator core between the first and second laminations.
 21. The pumprecited in claim 9, further comprising a second spacer that encirclesthe rotor core and extends axially along a portion of the rotor corebetween the first and second magnet assemblies.
 22. The pump recited inclaim 9, further comprising: a Hall sensor for detecting the axialposition of the rotor relative to the stator and generates a positionsignal indicative of this position; a voltage to frequency convertorcircuit that modulates a carrier frequency that is in a band differentthan the frequency band used to control the motor, the position signalbeing carried to a motor controller at the carrier frequency over wiresthat are used to power the motor.
 23. The pump recited in claim 9,wherein the pump is configured such that fluid inlet pressures acting onthe first impeller exerts an axial force on the rotor assembly in afirst direction along the axis and fluid inlet pressures acting on thesecond impeller exerts an axial force on the rotor assembly in a seconddirection along the axis, opposite the first direction.
 24. The pumprecited in claim 23, wherein the axial forces exerted on the rotorassembly by the fluid inlet pressures acting on the first and secondimpellers adjusts the axial position of the rotor assembly to helpbalance the fluid inlet pressures acting on the first and secondimpellers.
 25. The pump recited in claim 9, further comprising a firstinlet associated with the first impeller, and a second inlet associatedwith the second impeller, the first and second inlets having differentinternal diameters.
 26. The pump recited in claim 25, wherein theinternal diameters of the first and second inlets are selected to be ofdifferent sizes that create differential inlet pressure drops to biasthe axial forces acting on the first and second impellers.